500
Find the area of a regular dodecagon (12-sided figure) with a side length of 5cm.
Hint: divide it into triangles
The regular dodecagon can be split into twelve congruent isosceles triangles with vertices meeting at
the center of the dodecagon. The interior angles of a dodecagon sum to 1800°, so each angle is 150°.
Since this is a regular dodecagon, the isosceles triangles will have base angles of 75°, and 2·tan 75° as the height of the triangle. Therefore, the area of the dodecagon is 12 ⋅ 0.5 ⋅ 4 ⋅ 2⋅ tan75 , or 179.14cm^2